1. Field of the Invention
The present invention relates to a Liquid Crystal Display (LCD) and method for manufacturing the same and, more particularly to, a transflective active-matrix type LCD having a transmission region and a reflection region in its pixel and method for manufacturing the same.
2. Description of the Related Art
Because of its features of a small and thin geometry and low power consumption, an LCD has been put to practical use in a variety of applications such as an OA apparatus and a portable apparatus. The LCDs are classified in a transmission type and a reflection type, the LCD of the transmission type of which has no function to emit light for itself unlike a CRT or an EL display and so is provided with a back-light source separately so that display may be controlled by transmitting/blocking the back-light of liquid crystal thereof.
Although the transmission type LCD can use back-light to obtain bright display independently of the surrounding environments, a back-light source thereof typically has large power consumption of substantially a half of the total consumption thereof, thus contributing to an increase in the overall power consumption. If the LCD is driven by a battery in particular, its operating time is decreased, while if a large sized battery is mounted thereto on the other hand, its total weight is increased, thus preventing improvements in size and weight thereof.
To solve this problem owing to large power consumption of the back-light source, a reflection type LCD is suggested which utilizes surrounding light for display. The reflection type LCD employs a reflecting plate in place of the back-light source to transmit/block the surrounding light reflected by the reflecting plate in order to control display, so that it need not have a back-light source, to thereby reduce its power consumption, size, and weight; at the same time, however, it is largely deteriorated in visibility problematically if the surroundings are dark.
Although the transmission type and reflection type LCDs have these advantages and disadvantages of their own, a back-light source is required in order to obtain stable display but inevitably increases power consumption of the LCDs if only it is used as the light source thereof. To solve this problem, for example, Japanese Patent Application (KOKOKU) Laid-Open No. Hei 11-101992 discloses a transflective type LCD which can suppress power consumption of its back-light source and secure visibility independently of the surrounding environments, in which a transmission region and reflection region are provided in each pixel thereof to enable providing transmission mode display and reflection mode display on a single liquid crystal panel.
A conventional transflective type LCD is described as follows with reference to FIG. 18. FIG. 18 is a cross sectional view of conventional transflective type LCD.
As shown in FIG. 18, the conventional transflective type LCD comprises an active matrix substrate 12 on which a switching element such as a Thin Film Transistor (hereinafter abbreviated as TFT) 3 is formed, an opposing substrate 16 on which a color filter, a black matrix, etc. are formed, a liquid crystal layer 17 sandwiched by these substrates, and a back-light source 18 arranged below the active matrix substrate 12.
On the active matrix substrate 12 is provided with a gate line and a data line and, near an intersection thereof, a TFT 3, in such a configuration that a drain electrode 2a and a source electrode 2b of the TFT3 are connected to the data line and a pixel electrode respectively. Each pixel is divided into a transmission region which transmits back-light and a reflection region which reflects surrounding light in such a construction that the transmission region has a transparent electrode film 5 formed on a passivation film 10 and the reflection region has a reflection electrode film 6 made of metal on an irregular film 11 made of an organic substance.
In this construction of the transflective type LCD, in the transmission region, back-light radiated from a back side of the active matrix substrate 12 passes through the liquid crystal layer 17 and is emitted from the opposing substrate 16, while in the reflection region, surrounding light injected through the opposing substrate 16 once enters the liquid crystal layer 17 and is reflected by the reflection electrode film 6 and passes back through the liquid crystal layer 17 and then is emitted from the opposing substrate, so that there occurs a difference in optical path length between the transmission region and the reflection region.
To guard against this, conventionally, a polarization state of the emitted light has been adjusted so as to equalize the optical path lengths of the liquid crystal layer 17 in these two regions to each other by forming the organic irregular film 11 in the reflection region thicker than that in the other so that the gap of the liquid crystal layer 17 in the reflection region may be substantially a half of that in the transmission region.
Generally, the gradation-luminance characteristics of the liquid crystal panels need to be the same in the transmission region and the reflection regions so that an image impression in the transmission mode may match that in the reflection mode. For this purpose, the voltage-luminance characteristics (V-T) of the panel in the transmission mode may agree with those in the reflection mode.
In the above-mentioned conventional transflective type LCD, however, a gap of the liquid crystal layer 17 is different in the reflection region and the transmission region, that is, the gap with respect to the electrode is different on the side of the active matrix substrate 12 and on the side of the opposing substrate 16, so that the strength of an electric field applied on the liquid crystal cannot be equal in the various regions, to result in a change in luminance in these regions, thus problematically deteriorating the display quality.